Apparatus and method for introducing material into electric discharge devices



APPARATUS AND METHOD FOR INTRODUCING M ATERIAL INTO ELECTRIC DISCHARGEDEVICES Filed Feb. 28, 1935 Oct. 26, 1937. WYA. RUGGLES 2,097,307.

VA POR/ ZABL E MA TE R/AL.

\ ELECTRIC HEA TERS Inventor 53 William A.Rugiles, M H/ 7-! W 6 H is.Attorneyatented Oct. 26, 1937 UNITED STATES APPARATUS AND METHOD FORINTRODUC- ING MATERIAL INTO ELECTRIC DIS- CHARGE DEVICES I William A.Ruggles, Schenectady, N. Y., assignor to General Electric Company, acorporation of New York Application February 28, 1935, Serial No. 8,631

2 Claims. (Cl. 250-275) The present invention relates to electricdischarge devices, more particularly to improved methods for introducinginto vacuum tubes materials which are either deleteriously affected bythe atmosphere or are difilcult to handle. Another object of theinvention is to provide an improved practical method for preparing andstoring material which is to be introduced into vacuum tubes for'gettering 'or for activating purposes.

I have chosen to illustrate and describe my invention in connection witha typical type of electric discharge device and in particular a lamp inwhich light is produced bygthe passage of electricity through anattenuated gas consisting, at least in part, of vaporized metal'whichvolatilizes at a relatively low temperature, for example sodium.

Sodium is a very active material and when exposed to the atmosphere,takes up moisture and oxidizes-rapidly. Alkali metals of this sort arevery diflicult to obtain in a pure state and even more diflicult tointroduce, without sacrificing purity, into an electric dischargedevice. In certain types of devices, such as glow lamps and othergaseous discharge devices, it is sometimes necessary that the amount andkind of active material introduced therein be accurately controlled inorder that the light quality of the lamps and the electricalcharacteristics of the other devices made in quantity production may notvary but will be of a'predetermined and reproducible character. Thepresent invention provides a practical method of accomplishing theseresults and in particular, of assuring not only a high degree of freedomfrom contamination of the active material when introduced into theenvelope but also of assuring that the quantity of the material is of apredetermined weight or volume, or at least, falls within narrowpermissible ranges of weights or volumes.

The invention will be more fully explained in connection with theaccompanying drawing in which Fig. 1 is a elevational view, partly insection, of a vapor lamp in which an active material is to beintroduced. Fig. 2 is a diagrammatic view of apparatus useful incarrying out the invention, and Fig. 3 is an elevational view of astructure from which a capsule is formed.

Referring to Fig. 1, the lamp thereillustrated comprises a tubularmember I consisting of sodium-resistant glass, or lined with asodiumresistant glass. In the envelope, there is provided an attenuatedgas, ordinarily a rare gas such as neon, and a small quantity ofsodium.While sodium may be introduced in any convenient manner, I prefer toutilize the capsule method so-called, which will be described in detaillater. For this purpose, a capsule 2 is provided and containing a fewtenths of a gram of metallic sodium. The capsule is preferably formed inthe manner described hereinafter out of thin glass which is bothheat-resistant and alkali-resistant. A glass sold under the name ofCorning 705 AJ has been found to be suitable for this purpose. Thesodium is preferably introduced near the center of the lamp so that thesodium escaping from the capsule, as will bepointed out hereinafter. isdeposited on the mid-portion of the tube. v

Surrounding the envelope I is a-transparent heat conservator 3 which, asshown in the drawing, consists of a double-walled vessel havingsubstantially th same shape as the lamp envelope and closely surroundingit. The heat conservator preferably is evacuated.

The several electrode structures 4, 5 are provided at opposite ends ofthe envelope i, each functioning alternatively as cathode and anodeduring the operation of the lamp on alternating current circuits. Theelectrode structure 4 consists of a filamentary spiral 6 connected tothe leading-in conductors l, 8 and surrounded by a metal member 9 havinga flattened cylindrical conflguration'and which as illustrated, iselec-' trically connected to the leading-in conductor 8. When theelectrode structure 4 operates as a cathode, electrons are emitted bythe spiral member 6 which is heated to an electron-emitting temperatureby current supplied through the sealed-in conductors i0, H from anysuitable source (not shown). In order to enhance the electron emissivityof the heated member 6, it is preferably coated with alkaline earthmaterial, suchfor example as barium oxide in accordance with well-knownpractice. During the half-wave period when the electrode structure 4 isoperating as a cathode, the cylindrical member 9 which surrounds theheated portion may emit some electrons, particularly so when itsinterior surface is also coated with emisslve material'such as bariumoxide. but in the main it is a function of the member 9 to act as anodeduring the reverse half-cycle when the electrode 4 is at a positivepotential.

The electrode structure 5 at the opposite end of the lamp has aconstruction similar to the electrode structure 4. It is supported by apair of parallel conductors which extend throughout the length of thelamp envelope and are surrounded by suitable insulating jackets it, as,

consisting, for example, of alumina or beryllia. Current for heating thefilamentary spiral member H of the electrode structure 5 is suppliedthrough the .external conductors II, I! from some suitable source (notshown). The electrode structure 5 is surrounded by a metal cyl lnder 2|preferably of flattened configuration which acts as anode during thehalf-cycle when the electrode 5 is at positive potential. This structureis prevented from vibrating by an anchor 22 which is secured to theinsulating coatin gs l3, H by the supports 23, 2.

In operation, when alternating voltage is impressed between theelectrodes 4, 5 and the filaments 6 and I! are suitably energized, thelamp gives off an intense but soft yellow light, assuming the material 2to be sodium. In order to start the lamp at reasonably low voltages, astarting anode 25 may be provided to which connection is made from theexterior by means of a leading-in conductor 28. This electrode mayconsist of a metal sleeve surrounding one of the insulating Jackets i3,I4 and in operation, takes the .function of auxiliary anode positionedfairly close to the spiral 8 which serves as a cathode during thestarting period.

A lamp structure such as described has been disclosed and claimed in apatent application filed July 7, 1934, in the name of Gorton R. Fondaand Andrew H. Young, Serial No. 734,090, entitled Method of operating.vapor electric lamps" and assigned to the same assignee as the presentinvention.

It is apparent that in a lamp of this type it is essential that thesodium or other luminosityproducing material be absolutely pure becausethe slightest amount of impurity, for example the oxide or hydroxide,may have a deleterious effect on the activity of the cathode, even tothe extent of de-activating the same and thereby reducing the lightintensity of the lamp'as well as materially shortening its life.Furthermore, in certain types of tubes,,the amount of active materialintroduced therein may also have a profound efiect on theelectricalcharacteristics of the tube. The present invention, therefore, isdirected to an improved method for introducing sodium or similarmaterial into devices in which the introduced material must be of thehighest degree of purity. and of a definite and predetermined quantity.

In general, the improved method contemplates the use of a capsuleconstituted of a readily frangible material or having a frangibleportion, and filling the capsule with sodium or other material in such amanner as to remove all foreign substances and also to prevent anyadulteration and contamination of pure material. Thereafter the capsuleis mounted in an electric discharge device and the material released atthe proper time during or after the manufacturing schedule of the tubesimply by breaking the capsule and permitting the material to leave thecapsule bodily and practically instantaneously.

Inthe practice of my invention, I prefer employ a multi-distillationprocess in which sodium is successively transported either in the liquidor vapor phase, or both, through several compartments and finally isforced into one or more capsules. As shown in Fig. 2, apparatus whichmay be successfully used for this purpose constitutes a closed systemhaving only two openings, one of which may be connected to a pump forevacuating the system and the other to a gas supply for providing thenecessary pressure communicating with a bulbous receptacle 2|;

This receptacle is joined to another bulbous receptacle 29 through apiece of tubing 30, and fused to the receptacle 28 there is an angularpieceof glass tubing 3| which is joined to a manifold member 32 also ofglass. A tubulation 33 is taken from the upper left-hand corner (asshown) of the manifold 32 and this tubing terminates in two smallertubuiations 34 and 35, each of which is provided with a stopcock 35 or11 respectively. The lower end of the manifold 32 terminates in aplurality of outwardly and downwardly extending tubulations ll to whichthe capsules 39 may be fused in any suitable and well-known manner. Asshown, three such capsules are secured to each of the tubulatlons 38.

Fig. 3shows an enlarged view of one of these capsules. The capsulespreferably take the form of a spherical or bulbous member made of suitable glass such as Corning 705 AJ and having a diameter of approximately96". From this member, there extends a glass capillary tubing 40 ofabout 5 millimeters diameter and long. This tubing has a central bore ofabout 4% millimeters diameter. The capsules are fabricated separatelyfrom the remainder of the apparatus and thereafter fused in any suitableand wellknown manner tothe tubulations 38. While these capsules may bemade in any suitable and wellknown manner, I have found it preferable toform the bulbous portion in a mold, and this may be conveniently done byfirst sealing one end of a capillary tubing of the same size as theextension 40 and after heating the closed end of the tubing, the latteris placed in a mold of suitable shape. The glass-blower then blows intothe open end of the tubing until the other end conforms to the shape ofthe mold which in the illustrative case is spherical. The excess lengthof capillary may be cutofi, leaving an extension of suitable lengthsecured to the spherical portion. Before the capsule is fused to thetubulation fl, it should preferably be given a test to determine thethickness of the wall of the sphere. For this purpose, the so-calledbump test has been found to be satisfactory. These tests are conductedwithin a yer-- tically mounted glass tube (not shown) resting on a heavyglass plate (not shown). tube has an interior diameter or bore somewhatlarger than the capsuleso as not to introduce any cushioning effects.The capsule is suspended within the glass tube, at the upper end thereofand released, thereby failing the length of the tube and striking theglass plate at the bottom. If the glass of the capsuleis of the properthickness the necessity for which will appear hereinafter, the capsulewill bounce a-"certain height within the tube. The proper height may bedetermlned by experiment; The preferred thickness of a capsulecontaining a few tenths of a gram of sodium is of the order of .007",although it will be understood that when greater amounts of sodium areemployed, the thickness may be increased correspondingly. The thicknessof glass will usually be less than .010". If the glass is less than thepredetermined thickness found to be necessary, the distance throughwhich the capsule falls may be so regulated as'to cause the capsule tobreak, whereas if the glass wall is too thick, the capsule will bouncetoo high.

The glass arm 34 may communicate with a The vertical pump (not shown)and the arm 33 is preferably secured to a receptacle containing a gassuch as neon which is inert with respect to the material being driventhrough the system into the capsules. 7

As shown in Fig. 2, under each of the bulbous members28, 23, there is anelectric heater M of any suitable and well-known design which ispreferably enclosed in a heavy metal plate 42 presenting a fiat surfaceto the spherical members 28 and 29.

The sodium or other active material isillustrated as taking the form ofchunks 43 contained within the glass tube 2! and indicated genericallyby the clause "vaporizable material. In the case of sodium, which isextremely diflicult to handle, it has been found convenient to employ astocking 43 made of metal gauze of fairly fine mesh, this stockinghaving a configuration as to fit snugly within the tube 21. In order tointroduce the active material, the stocking is filled with the materialwhile positioned away from the remainder of the apparatus, and the tube21 is temporarily open at the top to allow insertion of the stockingmember therein, after which the tube 21 is closed by a flame. In thecase of sodium, it is necessary to work with the greatest dispatch inplacing the active material 'within the stocking so that the materialwill not be exposed to the atmosphere any longer than is necessary.

Assuming that all of the capsules 39, after being tested in the mannerdescribed hereinbefore, have been secured to the tubulations 38 so thatthe lower end of the manifold member 32 is closed to the atmosphere, thestopcock 3! is closed and the stopcock 33 is opened to the pump. Thelatter may be of any convenient type and provided with the usualpressure gages so that the entire glass system is eventually evacuatedto as high a degree as desired. When the necessary vac.- uum has beenobtained, the sodium or other vaporizable material 63 is subjected toheat, externally applied through the glass tube 21, preferably by meansof an oven surrounding the tube. In the case of sodium, the material 43melts at about 250 C. and falls as a liquid into the bottom of thebulbous receptacle 28. The heaters M maintain the receptacles 28 and 29at an elevated temperature, sufficiently high to cause the melted sodium65 in the receptacle 23 to be distilled first into the receptacle 29 andthen redistilled into the tubulation 3!, then through the manifold 32,finally becoming lodged in the tubulations 38. The latter are maintainedat a relatively low temperature, e. g. of the order of the roomtemperature during the time that the sodium is passing through themelting and the distillation stages, consequently, the sodium 'tends tocondense over the interior surface of the tubulations 38. When all ofthe sodium has collected at the places mentioned, the pump is cut oil byturning the stopcock 36, and the stopcock 31 is turned to its onposition, permitting inert gas such as neon to pass through the tubes35, 33 into the manifold 32 and the tribulations 38. At the same time,the tubulations 38 are heated, preferably by means of a Bunsen flame,which causes the sodium to be converted into vapor and under thepressure exerted by the gas, to be forced through the capillaries 40into the capsules 39. The sodium immediately condenses and solidifies inthe capsules, and the torching and gas-admitting operations aremaintained until the proper amount of sodium has collected in each ofthe capsules. It is desirable that the capsules shall not be filled upcompletely with sodium. The height of the material in each capsule maybe visually determined whereby the volume of the material in therespective capsules is accurately controlled because the capsules are ofsubstantially the same volume content. This visual method of determiningthe amount of sodium in each capsule is so accurate that errors of onlyless than a fewper cent in volume are made. For the size of capsulegiven hereinbefore, approximately from 1.3 to 1.5 grams of sodium arecontained therein. The exact amount of sodium per capsule depends uponthe use to which the capsule is to be put and whether or'not the sodiumis to be used for producing luminosity in'a tube or for serving astrictly gettering purpose.

After the capsules have been filled to the proper level, as determinedinitially by experiment and later by observation, the cock 31 is turnedto its 05 position, thus cutting oil the gas supply and the cook 36turned on, connecting the system again to the pump. The capsules maythen be disconnected from the system by means of a Bunsen flame or torchplayed upon the respective capillaries 4B in such a manner as nottoreduce or destroy the vacuum within the system.

In view of the foregoing, it is apparent that the glass system shown inFig. 2 first permits the vaporizable material 43 to be melted and topass into the distillation chambers 28' and 29 where, after successivedistillation and causing the sodium to pass into successive vaporphases, the sodium finally reaches the capsules 39 in a highly distilledand pure state. The impurities originally present in the sodium are ofcourse collected at the various receiving points and do not enter into avapor phase, at least not at the temperatures employed, consequently,are not transported through the system into the capsules. 'It has beenfound in practice that the mesh stocking member 44 collects the largestbulk of the slag or other impurity and that additional impurities aresuccessively 29, also in the manifold 32. In addition to collectingforeign matter contained within the sodium, the stocking member 44 alsoserves the purpose of holding the chunks of sodium within the tube 29 sothat only material in melted form is permitted to drop into the chamber28. For this purpose, the stocking member 44 is par tially closed at thebottom by a transverse mesh member through which sodium in liquid formmay pass. When the openings in this transverse member become clogged bythe impurities, the stocking member is replaced.

For the closed system shown in Fig. 2, it is necessary that the glassshall be of the alkaliresistant type in case sodium or similar materialis being melted and distilled. Such a glass is well known in the art andlends itself to all of the ordinary glass-blowing operations.

If des red, the capsules may be used simply as convenient receptaclesfor storing the alkali or similar metal because the atmosphere ispositively precluded from reaching the purified material. However, inthe present illustrative case, the confinement of the sodium in a glasssheath or capsule is for the purpose of introducing the sodium in a purestate within an electric discharge device, typified by the lamp shown inFig. 1. As stated hereinbefore, the loaded capthe lamp. The latter maythen be disconnected from the pump, assuming that all of the electrodeshave been mounted in place and the lamp has been given the usualbake-out at a temperature of approximately 500 C. in order to removeoccluded gases, etc. The necessary inert gas is then admitted to theenvelope. If the wall thickness of the capsule 2 is suiilicientv towithstand the vapor pressure of the alkali metal within the capsule, thelatter will remain intact during this heat treatment and will not allowthe sodium to escape. v

Assuming the improved capsule 2 to be in proper position, the lamp isenergized or otherwise heated to a temperature suiilciently high tocause the sodium in the capsule to liquefy. The envelope is then given aviolent shaking, sufficient to break the capsule by causing it to strikeagainst the envelope. The capsule immediately shatters if the glass isof the proper thickness, permitting the sodium to escape instantaneouslyand in bulk and to flow over the mid-portion of the envelope. As theenvelope cools down, the sodium immediately condenses on this portionwhere it would normally collect after each operation of the lamp, due totheiact that the mid-portion of the envelope is cooler than the endportions. The glass content of the capsule is so small that all thatremains of it after shattering is simply a flne glass powder which doesnot aflect, even in the slightest degree, either the quality or thequantity of light given of! by the lamp.

While I have described my invention more especially in connection with acondition in which the sodium serves the purpose of aluminosity-producing material, it will be understood that the sodium orother alkali metal may be used for other purposes, for example, as agetter. The improved capsule method in which the wall of the capsule isshattered and the contained material instantaneously released isparticularly advantageous in cases where it is desired that the fulleffect of the active material shall be immediately available at theproper time for consponsor trolling or otherwise modifying the characterof the discharge between two or more electrodes within a sealedenvelope. It will also be understood that the present invention is notlimited to sodium or any other alkali metal but con-- templates the useof any material which must be provided in an ultra-pure state or onewhich is diiiicult to handle or which may readily combine with the gasesof the atmosphere. Indeed, the frangible capsule may enclose a body ofgas and after being introduced into a tube, the gas may be' released byshattering the capsule at any time during the manufacture of the tube orafterwards. Liquid materials such as mercury may also be introduced intoa tube'in this manner and the mercury purified by one or moredistillation steps before being placed in glass capsules.

As stated hereinbefore, the glass capsule provides a most convenient andeffective manner of storing active materials, solid, liquid or gas, overlong periods of time, at the end of which the capsule is quite asadaptable to use as a means for introducing the material into anelectric discharge device as it was when the capsule was originally madeand filled. I The apparatus employed in carrying out this process isextremely simple and inexpensive, calling for the services only of askilled glass-blower and yet the quality of the capsule and containedmaterial is uniformly of a high standard.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

a 1. A lamp comprising a sealed envelope containing an inert gas, aplurality of cooperating electrodes and a quantity of sodium containedwithin a glass capsule having a wall thickness less than .010" so as tobe completely shattered when struck against the envelope and therebypermitting the sodium to escape instantaneously and completely. p

2. A capsule containing alkali metal and composed of glass having a wallthickness less than WILLIAM A. RUGGLES.

